Volunteers will visit the laboratory for a screening visit during which s/he will sign the informed consent form, and undergo both physical and psychiatric exams. The second, third, fourth, and fifth visits will involve pre-study assessments, a standard breakfast, questionnaire sets, drug treatment, one scanning session, and lunch. After a baseline period during which participants will answer computerized questionnaires, they will receive a study medication (zolpidem [10 mg], alprazolam [1 mg], caffeine [200 mg], or placebo) and then answer the questionnaires. At 60-min post-medication, participants will be positioned within the scanner, and while in there they will perform tasks, blood pressure/heart rate will be monitored continuously, and an eye-tracking device will assess if their eyes are open. The scanning session will last approximately 1 hr, and it will be followed by hourly questionnaires sets until 6-hrs post-medication. Participants will take a taxicab home at that time. The entire visit will last approximately 8 hrs.